首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   243622篇
  免费   2948篇
  国内免费   1243篇
电工技术   4856篇
综合类   264篇
化学工业   35441篇
金属工艺   10864篇
机械仪表   7070篇
建筑科学   6239篇
矿业工程   481篇
能源动力   6276篇
轻工业   24156篇
水利工程   1836篇
石油天然气   1335篇
武器工业   3篇
无线电   31054篇
一般工业技术   44890篇
冶金工业   50128篇
原子能技术   3868篇
自动化技术   19052篇
  2021年   1566篇
  2019年   1425篇
  2018年   2321篇
  2017年   2224篇
  2016年   2444篇
  2015年   1908篇
  2014年   3160篇
  2013年   10796篇
  2012年   5452篇
  2011年   7791篇
  2010年   6292篇
  2009年   6969篇
  2008年   7565篇
  2007年   7664篇
  2006年   7033篇
  2005年   6522篇
  2004年   6245篇
  2003年   6267篇
  2002年   6246篇
  2001年   6377篇
  2000年   5805篇
  1999年   6422篇
  1998年   16569篇
  1997年   11605篇
  1996年   8953篇
  1995年   6690篇
  1994年   5908篇
  1993年   5728篇
  1992年   4054篇
  1991年   3998篇
  1990年   3587篇
  1989年   3507篇
  1988年   3441篇
  1987年   2910篇
  1986年   2842篇
  1985年   3416篇
  1984年   3053篇
  1983年   2747篇
  1982年   2548篇
  1981年   2569篇
  1980年   2431篇
  1979年   2273篇
  1978年   2235篇
  1977年   2809篇
  1976年   4172篇
  1975年   1900篇
  1974年   1797篇
  1973年   1784篇
  1972年   1461篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Discusses issues and interventions for working with adolescents who live in stepfamilies. A developmental perspective, using psychoeducation and brief strategic intervention approaches, is proposed for working with stepfamilies. Six major issues for adolescents in stepfamilies are discussed: developmental issues, sexuality issues, parent–child relationships, parenting in stepfamilies, nonresidential parent–child issues, and changes in visitation and custody. Case illustrations and suggested interventions are presented for each of these areas. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
962.
Of the several sources of acoustic information for distance perception, those arising from motion of the listener or sound source have received little attention. This motion-related information (recently called acoustic tau) is described, and experiments evaluating its utilization are presented. Accuracy and consistency at walking to the locations of briefly presented sounds were better when people listened while walking than while standing still. Manipulations of the sound to simulate shorter or longer target distances produced appropriate undershooting but not overshooting. The results indicate that people use motion-related acoustic information about distance to guide their locomotor actions, although they do not take full advantage of this information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
963.
A method for line interference reduction to be used in signal-averaged electrocardiography (SAECG) systems is proposed and its performance is analyzed. This new method is an adaptation of a previously reported technique for removal of line interference from conventional electrocardiograms. It involves the recording of a line reference signal simultaneous with the lead signals, so that a shifted and sealed version of it can be used to subtract line interference from the leads. It is shown that this line interference subtraction method can reduce line interference effectively and without introducing any additional noise into the ECG signal. It is also shown that Late Potential diagnostic decisions are not altered when this filter is applied. It is recommended that this technique be used in SAECG when line interference is unavoidable  相似文献   
964.
A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented  相似文献   
965.
966.
Previously established dose-response curves indicated that modafinil 20-40 mg/kg i.p. elicited in mice an obvious stimulation of locomotor activity roughly similar to that induced by (+)amphetamine 2-4 mg/kg. The effects of various agents modifying dopamine transmission were compared on the locomotor response to both drugs. The preferential D2 dopamine receptor antagonist haloperidol 37.5-150 micrograms/kg i.p. suppressed the stimulant effect of (+)amphetamine in a dose dependent manner, but not that of modafinil. The D1 dopamine receptor antagonist SCH 23390 (7.5-30 micrograms/kg s.c.) reversed the (+)amphetamine but not the modafinil induced hyperactivity. The tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (200 mg/kg) suppressed the hyperactivity induced by 4 mg/kg dexamphetamine but not that induced by 20 mg/kg modafinil. Associating L-DOPA 150 mg/kg and benserazide 37.5 mg/kg with (+)amphetamine 2 mg/kg resulted in stereotyped climbing behavior, that was not observed with modafinil 10-80 mg/kg. The profound akinesia induced by reserpine (4 mg/kg s.c.; 5 h before testing) was reversed by (+)amphetamine 2 mg/kg but not by modafinil 40 mg/kg. Finally, on synaptosomes prepared from mouse striata preloaded with [3H]dopamine, modafinil 10(-5) M did not increase the spontaneous [3H]dopamine release whereas (+)amphetamine, at the same concentration, doubled it. From all these differences between the two drugs, it is concluded that the mechanism underlying the modafinil induced stimulant locomotor effect differs completely from that of (+)amphetamine.  相似文献   
967.
968.
We investigated intestinal ethanol absorption in rats pretreated with saline, cyanamide, 4-methylpyrazole and cyanamide + 4-methylpyrazole. The value of the absorption rate constant in the cyanamide-pretreated group with high acetaldehyde levels was the lowest among the four groups, but there were no significant differences among the remaining groups. We found that high acetaldehyde concentration itself clearly reduces intestinal ethanol absorption.  相似文献   
969.
In this paper we investigate the impact of finite laser linewidths (i.e. source partial coherence) on the crosstalk performance of optical frequency division multiplexing (OFDM) networks employing single-cavity Fabry-Perot demultiplexers. Results are presented that show the important limitation imposed by the finite laser linewidths on the attainable bit error rate (BER), maximum number of users, and the required power penalties to overcome this impairment  相似文献   
970.
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号